An invasive species is one that is not native and whose introduction causes harm, or is likely to cause harm to Michigan's economy, environment or human health.

Many non-native species in Michigan, including fruits, vegetables, field crops, livestock and domestic animals, are important to our economy and lifestyle. Most non-native species are not harmful and may provide economic benefits. Invasive species cause harm when they outcompete native species by reproducing and spreading rapidly in areas where they have no natural predators and change the balance of the ecosystems we rely on.

Most invasive species find their way here with the help of humans.

• Modern means of transportation bring goods, services, people and invasives to all reaches of the globe.
• Ballast water from ships is to blame for introducing many invasive organisms to Great Lakes waters.
• Some exotic pets and plants that escape into the wild adapt to local conditions.
• Insects arriving from abroad in wood packing materials and wood products have caused irreparable damage to native trees and forests.
• Some invasives were brought to the U.S. intentionally as biological controls for other invasives or nuisance species; others were introduced as game or food species.

What makes many invasives so successful is their ability to colonize new areas very rapidly.

• For plants, this can mean having seeds that are eaten and distributed by birds, such as autumn olive, seeds that easily disperse or catch on clothing or fur, or plant parts that can reproduce whole plants from cut or broken pieces, like Eurasian watermilfoil.
• Oak wilt spores and emerald ash borer larvae have been transported to many sites in Michigan on firewood.
• Microscopic zebra mussel larvae and many invasive aquatic plants have hitchhiked from one lake to another on watercraft and trailers.
• Garlic mustard has spread along many roadsides and forest trails with the help of cars, plows, ATVs and hikers.
• For many invasives, hitchhiking with humans is a common mode of transportation.

Invasive species on the watch list have been identified as being an immediate and significant threat to Michigan's natural resources. These species either have never been confirmed in the wild in Michigan or have a limited known distribution.

Some invasive species are legally designated by the State of Michigan as either “prohibited” or “restricted”. If a species is prohibited or restricted, it is unlawful to possess, introduce, import, sell or offer that species for sale as a live organism, except under certain circumstances.

• The term “prohibited” is used for species that are not widely distributed in the state. Often, management or control techniques for prohibited species are not available.
• The term “restricted” is applied to species that are established in the state. Management and control practices are usually available for restricted species.

Michigan’s Natural Resources Environmental Protection Act (Part 413 of Act 451) established the list of prohibited and restricted species, which is regularly amended by Invasive Species Orders.